Method of replacing a printhead in an inkjet printer with minimal ink wastage

ABSTRACT

A method of replacing a printhead in an inkjet printer with minimal ink wastage, the method comprising the steps of:
         (i) providing a printhead comprising:
           an ink distribution manifold having an ink inlet and an ink outlet;   one or more printhead integrated circuits mounted on the manifold, each printhead integrated circuit comprising a plurality of nozzles;   
           (ii) providing an ink supply system comprising:
           an ink chamber in fluid communication with the ink inlet via an upstream ink line;   a reversible air pump communicating with a headspace of the ink chamber; and   a downstream ink line connected to the ink outlet;   
           (ii) actuating the pump so as to negatively pressurize the headspace, thereby depriming the printhead by drawing ink from the downstream ink line and the printhead into the ink chamber;   (iii) deactuating the pump and allowing an ink level in the ink chamber to equalize with an ink level in the upstream ink line;   (iv) removing the printhead from the printer, the removing including disconnecting the ink inlet and the ink outlet from respective upstream and downstream ink lines;   (v) replacing the printhead with a replacement printhead, the replacing including connecting an ink inlet and an outlet inlet of the replacement printhead with respective upstream and downstream ink lines;   (vi) actuating the pump so as to positively pressurize the headspace, thereby priming the printhead by drawing ink from the ink chamber, through the printhead and into the downstream ink line; and   (vii) deactuating the pump and allowing an ink level in the ink chamber to equilibrate to a predetermined level.

FIELD OF THE INVENTION

The present invention relates to printers and in particular inkjetprinters. It has been developed primarily to provide a fluidics systemwhich controls a hydrostatic ink pressure during normal printing, whilstenabling priming and depriming for printhead replacement.

CO-PENDING APPLICATIONS

The following applications have been filed by the Applicantsimultaneously with the present application:

-   -   SBF013US SBF014US SBF015US SBF016US SBF017US SBF018US SBF019US        SBF020US SBF021US SBF022US SBF024US SBF025US SBF026US SBF027US

The disclosures of these co-pending applications are incorporated hereinby reference. The above applications have been identified by theirfiling docket number, which will be substituted with the correspondingapplication number, once assigned.

CROSS REFERENCES

The following patents or patent applications filed by the applicant orassignee of the present invention are hereby incorporated bycross-reference.

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11/688866 11/688867 11/68886811/688869 11/688871 11/688872 11/688873 11/741766 12014767 1201476812014769 12014770 12014771 12014772 12014773 12014774 12014775 1201477612014777 12014778 12014779 12014780 12014781 12014782 12014783 1201478412014785 12014787 12014788 12014789 12014790 12014791 12014792 1201479312014794 12014796 12014798 12014801 12014803 12014804 12014805 1201480612014807 12049371 12049372 12049373 12049374 12049375 61034147 11/48298211/482983 11/482984 11/495818 11/495819 11/677049 11/677050 11/67705111872719 11872718 12046449 61033357 7306320 11/934781 D528156 10/7601807111935 10/760213 10/760219 10/760237 7261482 10/760220 700266410/760252 10/760265 7088420 11/446233 11/503083 11/503081 11/51648711/599312 6364451 6533390 6454378 7224478 6559969 6896362 70577606982799 11/202107 11/743672 11744126 11/743673 7093494 7143652 70897977159467 7234357 7124643 7121145 7089790 7194901 6968744 7089798 72405607137302 11/442177 7171855 7260995 7260993 7165460 7222538 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728517011/048748 7008041 7011390 7048868 7014785 7131717 7284826 73311017182436 7104631 7240993 7290859 11/202217 7172265 7284837 706657311/298635 7152949 7334877 11/442133 7326357 7156492 11/478588 73316537287834 11/525861 11/583939 11/545504 7284326 11/635485 11/73039111/730788 11/749148 11/749149 11/749152 11/749151 11/759886 11/86566811/874168 11/874203 11971182 12021086 12015441 11965722 6824257 72704756971811 6878564 6921145 6890052 7021747 6929345 6811242 6916087 69051956899416 6883906 6955428 7284834 6932459 6962410 7033008 6962409 70136417204580 7032997 6998278 7004563 6910755 6969142 6938994 718893510/959049 7134740 6997537 7004567 6916091 7077588 6918707 69235836953295 6921221 7001008 7168167 7210759 7337532 7331659 7322680 69887907192120 7168789 7004577 7052120 11/123007 6994426 7258418 70142987328977 11/177394 7152955 7097292 7207657 7152944 7147303 73381477134608 7264333 7093921 7077590 7147297 20060038853 11/248832 11/24842811/248434 7077507 7172672 7175776 7086717 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11/83463511839541 11860420 11/865693 11/863118 11/866307 11/866340 11/86968411/869722 11/869694 11/876592 11/945244 11951121 11/945238 1195535811965710 11962050 12015478 12015423 12015434 12023015 12030755 1202564112056228 12036279 12031598 12050949 123056217

BACKGROUND OF THE INVENTION

The Applicant has developed a wide range of printers that employpagewidth printheads instead of traditional reciprocating printheaddesigns. Pagewidth designs increase print speeds as the printhead doesnot traverse back and forth across the page to deposit a line of animage. The pagewidth printhead simply deposits the ink on the media asit moves past at high speeds. Such printheads have made it possible toperform full colour 1600 dpi printing at speeds of around 60 pages perminute, speeds previously unattainable with conventional inkjetprinters.

Printing at these speeds consumes ink quickly and this gives rise toproblems with supplying ink to the printhead. Not only are the flowrates higher but distributing the ink along the entire length of apagewidth printhead is more complex than feeding ink to a relativelysmall reciprocating printhead. In particular, the hydrostatic inkpressure requires careful control to avoid printhead flooding. TheApplicant has previously described means for controlling hydrostatic inkpressure in an ink supply system for a pagewidth printhead (see U.S.application Ser. No. 11/677,049 filed Feb. 21, 2007 and U.S. applicationSer. No. 11/872,714 filed Oct. 16, 2007, the contents of which areherein incorporated by reference).

Additionally, the Applicant's design of high speed A4 pagewidth printersrequires periodic replacement of a printhead cartridge, which comprisesthe printhead. In order to replace a printhead cartridge, it isnecessary to deprime a printhead, remove the printhead from the printer,replace the printhead with a new replacement printhead, and prime thereplacement printhead once it is installed in the printer. Hence, theink supply system must be able to perform prime and deprime operationsefficiently and, preferably, with minimal ink wastage.

SUMMARY OF THE INVENTION

In a first aspect the present invention provides an ink supply systemfor supplying ink to an inkjet printhead at a predetermined hydrostaticpressure, said ink supply system comprising:

-   -   a pressure-regulating chamber having an outlet port connected to        an ink inlet of said printhead, said chamber comprising a float        valve configured for maintaining a predetermined level of ink in        said chamber, said level of ink controlling said hydrostatic        pressure; and    -   an ink reservoir connected to an inlet port of said        pressure-regulating chamber, said ink reservoir being positioned        above said predetermined level of ink.        Optionally, said hydrostatic pressure, relative to atmospheric        pressure, is defined as ρgh, wherein ρ is the density of ink, g        is acceleration due to gravity and h is the height of the        predetermined level of ink relative to the printhead.        Optionally, said pressure-regulating chamber is positioned below        said printhead, and said hydrostatic pressure is negative        relative to atmospheric pressure.        Optionally, said float valve comprises:    -   an arm pivotally mounted about a pivot;    -   a float mounted at one end of said arm; and    -   a valve head mounted at an opposite end of said arm,        wherein said valve head is positioned for sealing engagement        with a valve seat at said inlet port.        Optionally, said inlet port and said outlet port of said        pressure-regulating chamber are positioned towards a base of        said chamber.        In a further aspect the ink supply system further comprising a        printhead priming system.        In another aspect the ink supply system comprising:    -   an air pump communicating with a headspace above said ink in        said chamber; and    -   a valve positioned between said ink reservoir and said inlet        port,        wherein, in a priming configuration, said valve is configured to        be shut and said pump is configured to positively pressurize        said headspace thereby forcing ink from said chamber into an ink        inlet of said printhead.        Optionally, a sensor is positioned for sensing ink in a        downstream ink line connected to an ink outlet of said        printhead, said sensor cooperating with said pump such that said        pump is shut off when said sensor senses any ink.        In another aspect the ink supply system further comprising means        for controlling an amount of ink flowing from said downstream        ink line back into said pressure-regulating chamber.        Optionally, said means is selected from the group comprising:    -   an electronically-controlled valve;    -   a check-valve; and    -   a loop section passing below said predetermined level of ink in        said chamber.        Optionally, said sensor is an optical sensor.        In a further aspect the ink supply system further comprising        means for minimizing phantom sensing of ink caused by ink        bubbles in said downstream ink line.        In a further aspect the ink supply system comprising a        bubble-bursting box, said box comprising:    -   at least one bubble-bursting chamber having a respective chamber        inlet; and    -   an air outlet.        Optionally, said air outlet is open to atmosphere or said air        outlet communicates with a pump inlet of said air pump.        Optionally, said at least one bubble-bursting chamber is        dimensioned to promote expansion and bursting of ink bubbles        entering said chamber via said chamber inlet.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of said ink supply system.        Optionally, said bubble-bursting box comprises an air chamber in        fluid communication with said at least one bubble-bursting        chamber via an air channel defined in a roof of said box, said        air outlet being defined in said air chamber.        Optionally, said air channel is a hydrophobic serpentine channel        comprising at least one ink-trapping stomach, said air channel        minimizing transfer of ink to said air chamber when said box is        tipped.

Optionally, said pump is a reversible pump.

Optionally, in a de-priming configuration, said pump is reversed and inkis pulled from said printhead towards said pressure-regulating chamber.In a second aspect the present invention provides a priming system forpriming an inkjet printhead having an ink inlet, an ink outlet and aplurality of nozzles, said priming system comprising:

-   -   an ink chamber having an outlet port connected to said ink inlet        via an upstream ink line;    -   an air pump having a pump outlet communicating with a headspace        above said ink in said ink chamber;    -   a sensor positioned for sensing ink in a downstream ink line        connected to said ink outlet, said sensor cooperating with said        pump such that said pump is shut off when said sensor senses any        ink; and    -   means for minimizing phantom sensing of ink caused by ink        bubbles in said downstream ink line,        wherein, in a priming configuration, said pump is configured to        positively pressurize said headspace until said sensor senses        ink.        Optionally, said ink chamber is a pressure-regulating chamber,        and said priming system further comprises:    -   an ink reservoir in fluid communication with an inlet port of        said pressure-regulating chamber, said ink reservoir being        positioned above a level of ink in said chamber; and    -   a valve positioned between said ink reservoir and said inlet        port,        wherein, in said priming configuration, said valve is configured        to be shut.        Optionally, said pump is reversible for effecting de-priming        operations.        Optionally, in a de-priming configuration, said pump is reversed        and ink is pulled from said printhead towards said ink chamber.        Optionally, said ink outlet is in fluid communication with a        pump inlet, thereby enabling both pushing and pulling of ink        during a priming and/or a de-priming operation.        In a further aspect there is provided a priming system further        comprising means for controlling, after priming, an amount of        ink flowing from said downstream ink line back into said        pressure-regulating chamber.        Optionally, said means is selected from the group comprising:    -   an electronically-controlled valve;    -   a check-valve; and    -   a loop section passing below a level of ink in said chamber.        Optionally, said sensor comprises an optical sensor.        Optionally, said means for minimizing phantom sensing of ink        comprises a bubble-bursting box, said box comprising:    -   one or more bubble-bursting chambers having a respective chamber        inlet; and    -   an air outlet.        Optionally, said sensor is positioned to sense ink above a        bubble-bursting point in at least one of said bubble-bursting        chambers.        Optionally, said at least one bubble-bursting chamber is        transparent.        Optionally, said air outlet is:    -   open to atmosphere; or    -   in fluid communication with a pump inlet of said pump, thereby        enabling both pushing and pulling of ink through said printhead        during a priming or a de-priming operation.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of said ink supply system.        Optionally, each bubble-bursting chamber is dimensioned to        promote expansion and bursting of ink bubbles entering said        chamber via said chamber inlet.        Optionally, each bubble-bursting chamber has curved sidewalls,        wherein a curvature of said sidewalls is greater than a        curvature of said conduit.        Optionally, each bubble-bursting chamber is generally        crescent-shaped, thereby maximizing said curvature in a minimal        volume.        Optionally, said bubble-bursting box comprises an air chamber in        fluid communication with said bubble-bursting chambers via an        air channel defined in a roof of said box, said air outlet being        defined in said air chamber.        Optionally, said air channel is a hydrophobic serpentine channel        comprising at least one ink-trapping stomach, said air channel        minimizing transfer of ink to said air chamber when said box is        tipped.        Optionally, said printhead is replaceable.        Optionally, said printhead comprises one or more printhead        integrated circuits mounted on an ink distribution manifold,        each printhead integrated circuit comprising a plurality of        nozzles, and said manifold having said ink inlet and said ink        outlet.        In a third aspect the present invention provides a printer        comprising:    -   an inkjet printhead having an ink inlet, an ink outlet and a        plurality of nozzles;    -   an ink supply system for supplying ink to said inkjet printhead        at a predetermined hydrostatic pressure, said ink supply system        comprising:        -   a pressure-regulating chamber having an outlet port            connected to said ink inlet of said printhead, said chamber            comprising a float valve configured for maintaining a            predetermined level of ink in said chamber, said level of            ink controlling said hydrostatic pressure; and        -   an ink reservoir connected to an inlet port of said            pressure-regulating chamber, said ink reservoir being            positioned above said predetermined level of ink.            Optionally, said hydrostatic pressure, relative to            atmospheric pressure, is defined as ρgh, wherein ρ is the            density of ink, g is acceleration due to gravity and h is            the height of the predetermined level of ink relative to the            printhead.            Optionally, said pressure-regulating chamber is positioned            below said printhead, and said hydrostatic pressure is            negative relative to atmospheric pressure.            Optionally, said float valve comprises:    -   an arm pivotally mounted about a pivot;    -   a float mounted at one end of said arm; and    -   a valve head mounted at an opposite end of said arm,        wherein said valve head is positioned for sealing engagement        with a valve seat at said inlet port.        Optionally, said inlet port and said outlet port of said        pressure-regulating chamber are positioned towards a base of        said chamber.        In a further aspect the printer further comprising a printhead        priming system.        In another aspect the printer comprising:    -   an air pump communicating with a headspace above said ink in        said chamber; and    -   a valve positioned between said ink reservoir and said inlet        port,        wherein, in a priming configuration, said valve is configured to        be shut and said pump is configured to positively pressurize        said headspace thereby forcing ink from said chamber into an ink        inlet of said printhead.        Optionally, a sensor is positioned for sensing ink in a        downstream ink line connected to an ink outlet of said        printhead, said sensor cooperating with said pump such that said        pump is shut off when said sensor senses any ink.        In another aspect the printer further comprising means for        controlling an amount of ink flowing from said downstream ink        line back into said pressure-regulating chamber.        Optionally, said means is selected from the group comprising:    -   an electronically-controlled valve;    -   a check-valve; and    -   a loop section passing below said predetermined level of ink in        said chamber.        Optionally, said sensor is an optical sensor.        In a further aspect the printer further comprising means for        minimizing phantom sensing of ink caused by ink bubbles in said        downstream ink line.        In another aspect the printer comprising a bubble-bursting box,        said box comprising:    -   at least one bubble-bursting chamber having a respective chamber        inlet; and    -   an air outlet.        Optionally, said air outlet is open to atmosphere or said air        outlet communicates with a pump inlet of said air pump.        Optionally, said at least one bubble-bursting chamber is        dimensioned to promote expansion and bursting of ink bubbles        entering said chamber via said chamber inlet.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of said ink supply system.        Optionally, said bubble-bursting box comprises an air chamber in        fluid communication with said at least one bubble-bursting        chamber via an air channel defined in a roof of said box, said        air outlet being defined in said air chamber.        Optionally, said air channel is a hydrophobic serpentine channel        comprising at least one ink-trapping stomach, said air channel        minimizing transfer of ink to said air chamber when said box is        tipped.        Optionally, said pump is a reversible pump.        Optionally, in a de-priming configuration, said pump is reversed        and ink is pulled from said printhead towards said        pressure-regulating chamber.        In a fourth aspect the present invention provides a printer        comprising:    -   an inkjet printhead having an ink inlet, an ink outlet and a        plurality of nozzles;    -   a priming system for priming said printhead, said priming system        comprising:        -   an ink chamber having an outlet port connected to said ink            inlet via an upstream ink line;        -   an air pump having a pump outlet communicating with a            headspace above said ink in said chamber;        -   a sensor positioned for sensing ink in a downstream ink line            connected to said ink outlet, said sensor cooperating with            said pump such that said pump is shut off when said sensor            senses any ink; and        -   means for minimizing phantom sensing of ink caused by ink            bubbles in said downstream ink line,            wherein, in a priming configuration, said pump is configured            to positively pressurize said headspace until said sensor            senses ink.            Optionally, said ink chamber is a pressure-regulating            chamber, and said priming system further comprises:    -   an ink reservoir in fluid communication with an inlet port of        said pressure-regulating chamber, said ink reservoir being        positioned above a level of ink in said chamber; and    -   a valve positioned between said ink reservoir and said inlet        port,        wherein, in said priming configuration, said valve is configured        to be shut.        Optionally, said pump is reversible for effecting de-priming        operations.        Optionally, in a de-priming configuration, said pump is reversed        and ink is pulled from said printhead towards said ink chamber.        Optionally, said ink outlet is in fluid communication with a        pump inlet, thereby enabling both pushing and pulling of ink        during a priming and/or a de-priming operation.        In a further aspect the printer further comprising means for        controlling an amount of ink flowing from said downstream ink        line back into said pressure-regulating chamber.        Optionally, said means is selected from the group comprising:    -   an electronically-controlled valve;    -   a check-valve; and    -   a loop section passing below a level of ink in said chamber.        Optionally, said sensor comprises an optical sensor.        Optionally, said means for minimizing phantom sensing of ink        comprises a bubble-bursting box, said box comprising:    -   one or more bubble-bursting chambers having a respective chamber        inlet; and    -   an air outlet.        Optionally, said sensor is positioned to sense ink above a        bubble-bursting point in at least one of said bubble-bursting        chambers.        Optionally, said at least one bubble-bursting chamber is        transparent.        Optionally, said air outlet is:    -   open to atmosphere; or    -   in fluid communication with a pump inlet of said pump, thereby        enabling both pushing and pulling of ink through said printhead        during a priming or a de-priming operation.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of said ink supply system.        Optionally, each bubble-bursting chamber is dimensioned to        promote expansion and bursting of ink bubbles entering said        chamber via said chamber inlet.        Optionally, each bubble-bursting chamber has curved sidewalls,        wherein a curvature of said sidewalls is greater than a        curvature of said conduit.        Optionally, each bubble-bursting chamber is generally        crescent-shaped, thereby maximizing said curvature in a minimal        volume.        Optionally, said bubble-bursting box comprises an air chamber in        fluid communication with said bubble-bursting chambers via an        air channel defined in a roof of said box, said air outlet being        defined in said air chamber.        Optionally, said air channel is a hydrophobic serpentine channel        comprising at least one ink-trapping stomach, said air channel        minimizing transfer of ink to said air chamber when said box is        tipped.        Optionally, said printhead is a replaceable pagewidth printhead.        Optionally, said printhead comprises one or more printhead        integrated circuits mounted on an ink distribution manifold,        each printhead integrated circuit comprising a plurality of        nozzles, and said manifold having said ink inlet and said ink        outlet.        In a fifth aspect the present invention provides an ink sensing        device for an ink supply system, said device comprising:    -   a bubble-bursting box comprising:        -   one or more bubble-bursting chambers, each chamber having a            respective chamber inlet for connection to an ink line; and        -   an air outlet in fluid communication with each chamber; and    -   a sensor positioned to sense ink above a bubble-bursting point        in at least one of said bubble-bursting chambers,        wherein said device is configured to minimize phantom sensing of        ink caused by ink bubbles in said ink line.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of an ink supply system.        Optionally, each bubble-bursting chamber is dimensioned to        promote expansion and bursting of ink bubbles entering said        chamber via said chamber inlet.        Optionally, each bubble-bursting chamber has curved sidewalls,        wherein a curvature of said sidewalls is greater than a        curvature of a conduit defining said ink line.        Optionally, each bubble-bursting chamber is generally        crescent-shaped, thereby maximizing said curvature in a minimal        volume.        Optionally, said bubble-bursting box comprises a common air        chamber in fluid communication with each bubble-bursting        chamber, said air outlet being positioned in said air chamber.        Optionally, each bubble-bursting chamber communicates with said        air chamber via a respective air channel defined in a roof of        said box.        Optionally, each air channel is a serpentine channel for        minimizing transfer of ink to said air chamber when said box is        tipped.        Optionally, each air channel is hydrophobic.        Optionally, each air channel comprises at least one ink-trapping        stomach.        Optionally, each air channel terminates at a channel outlet        defined in a roof of said box, each channel outlet being        positioned to deposit ink into said air chamber.        Optionally, said air outlet is defined in a base of said air        chamber, and each channel outlet is offset from said air outlet.        Optionally, a snorkel extends from said air outlet towards said        roof, thereby maximizing an effective ink-collecting volume of        said air chamber.        Optionally, said air chamber has an air vent defined therein.        Optionally, said air chamber has one or more air vents defined        therein, the number of air vents regulating a pressure in said        bubble-bursting box when said air outlet is connected to a pump.        Optionally, said sensor is an optical sensor.        Optionally, said sensor provides a feedback signal for a pump        pumping ink into said bubble-bursting box.        Optionally, sensor senses ink in only one of said        bubble-bursting chambers.        Optionally, said one bubble-bursting chamber comprises a float        ball chamber in fluid communication with a primary        bubble-bursting chamber, said float ball chamber containing a        float ball, and said sensor optically sensing when said float        ball reaches a predetermined height.        In another aspect there is provided an ink supply system        comprising the bubble-bursting box comprising:    -   one or more bubble-bursting chambers, each chamber having a        respective chamber inlet for connection to an ink line; and    -   an air outlet in fluid communication with each chamber; and    -   a sensor positioned to sense ink above a bubble-bursting point        in at least one of said bubble-bursting chambers,        wherein said device is configured to minimize phantom sensing of        ink caused by ink bubbles in said ink line.        In a sixth aspect the present invention provided a        bubble-bursting box for bursting bubbles of a liquid entering        said box, said box comprising:    -   one or more bubble-bursting chambers, each chamber having a        respective chamber inlet for connection to liquid conduit, said        chamber inlet being defined in a base of each chamber; and    -   a common air chamber in fluid communication with each        bubble-bursting chamber, said air chamber having an air outlet        defined in a base thereof;    -   a cover for said bubble-bursting chambers and said air chamber,        said cover defining a roof of said box, said cover having one or        more air channels defined therein, each air channel providing        fluid communication between a respective bubble-bursting chamber        and said common air chamber.        Optionally, said liquid is ink.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of an ink supply system for a printer.        Optionally, each bubble-bursting chamber is dimensioned to        promote expansion and bursting of liquid bubbles entering said        chamber via said chamber inlet.        Optionally, each bubble-bursting chamber has curved sidewalls,        wherein a curvature of said sidewalls is greater than a        curvature of said liquid conduit.        Optionally, each bubble-bursting chamber is generally        crescent-shaped, thereby maximizing said curvature in a minimal        volume.        Optionally, each air channel is a serpentine channel for        minimizing transfer of liquid to said air chamber when said box        is tipped.        Optionally, each air channel is hydrophobic.        Optionally, each air channel comprises at least one        liquid-trapping stomach.        Optionally, each air channel terminates at a channel outlet        defined in a roof of said air chamber, each channel outlet being        positioned to deposit liquid into said air chamber.        Optionally, each channel outlet is offset from said air outlet.        Optionally, a snorkel extends from said air outlet towards said        roof, thereby maximizing an effective liquid-collecting volume        of said air chamber.        Optionally, said air chamber has an air vent defined therein.        Optionally, said air chamber has one or more air vents defined        therein, the number of air vents regulating a pressure in said        bubble-bursting box when said air outlet is connected to a pump.        Optionally, one of said bubble-bursting chamber comprises a        float ball chamber in fluid communication with a primary        bubble-bursting chamber, said float ball chamber containing a        float ball.        Optionally, at least one of said bubble-bursting chambers is        configured for use with an optical sensor, said optical sensor        sensing a level of liquid in said at least one chamber.        Optionally, said at least one bubble-bursting chamber is        transparent.        In a further aspect the present invention provided a liquid        sensing device comprising:    -   (A) a bubble-bursting box comprising:        -   one or more bubble-bursting chambers, each chamber having a            respective chamber inlet in a base thereof for connection to            liquid conduit; and        -   a common air chamber in fluid communication with each            bubble-bursting chamber, said air chamber having an air            outlet defined in a base thereof; and        -   a cover for said bubble-bursting chambers and said air            chamber, said cover defining a roof of said box, said cover            having one or more air channels defined therein, each air            channel providing fluid communication between a respective            bubble-bursting chamber and said common air chamber; and    -   (B) an optical sensor positioned to sense liquid above a        bubble-bursting point in at least one of said bubble-bursting        chambers.        Optionally, said device is configured to minimize phantom        sensing of liquid caused by liquid bubbles in said liquid        conduit.        Optionally, said box is transparent.        In a seventh aspect the present invention provided a printhead        depriming system, said system comprising:    -   an ink reservoir;    -   an ink chamber positioned below said ink reservoir, said ink        chamber comprising an outlet port connected to an ink inlet of        said printhead via an upstream ink line, an inlet port connected        to said ink reservoir, and a float valve configured for closing        said inlet port; and    -   an air pump communicating with a headspace above said ink in        said ink chamber, such that actuation of said air pump generates        a negative pressure in said headspace and draws ink from said        printhead into said ink chamber so as to de-prime said        printhead,        wherein an increased level of ink in said ink chamber during        said de-priming causes concomitant shutting of said float valve        and isolates said ink reservoir from said printhead.        Optionally, said printhead is positioned above said ink chamber.        In another aspect the depriming system further comprising a        downstream ink line connected to an ink outlet of said        printhead, wherein ink is drawn from said downstream ink line,        through said printhead and towards said ink chamber during said        de-priming.        Optionally, said downstream ink line is in fluid communication        with said air pump, thereby enabling both pushing and pulling of        ink through said printhead during said depriming.        Optionally, said pump is reversible for effecting both        de-priming and priming operations.        Optionally, a check valve is positioned between said ink        reservoir and said ink chamber for isolating said ink reservoir        from said printhead during a priming operation.        Optionally, said float valve comprises:    -   an arm pivotally mounted about a pivot;    -   a float mounted at one end of said arm; and    -   a valve head mounted at an opposite end of said arm,        wherein said valve head is positioned for sealing engagement        with a valve seat at said inlet port.        Optionally, said ink chamber is a pressure-regulating chamber        for regulating a hydrostatic pressure of ink supplied to said        printhead during normal printing.        Optionally, is configured for use with a replaceable pagewidth        printhead.        Optionally, said printhead comprises one or more printhead        integrated circuits mounted on an ink distribution manifold,        each printhead integrated circuit comprising a plurality of        nozzles, and said manifold having said ink inlet and an ink        outlet.        In another aspect the present invention provided a printer        comprising:    -   an inkjet printhead having an ink inlet and a plurality of        nozzles; and    -   a printhead depriming system, said depriming system comprising:        -   an ink reservoir;        -   an ink chamber positioned below said ink reservoir, said ink            chamber comprising an outlet port connected to said ink            inlet via an upstream ink line, an inlet port connected to            said ink reservoir, and a float valve configured for closing            said inlet port; and        -   an air pump communicating with a headspace above said ink in            said ink chamber, such that actuation of said air pump            generates a negative pressure in said headspace and draws            ink from said printhead into said ink chamber so as to            de-prime said printhead,            wherein an increased level of ink in said ink chamber during            said de-priming causes concomitant shutting of said float            valve and isolates said ink reservoir from said printhead.            Optionally, said printhead is positioned above said ink            chamber.            In a further aspect the printer further comprising a            downstream ink line connected to an ink outlet of said            printhead, wherein ink is drawn from said downstream ink            line, through said printhead and towards said ink chamber            during said de-priming.            Optionally, said downstream ink line is in fluid            communication with said air pump, thereby enabling both            pushing and pulling of ink through said printhead during            said depriming.            Optionally, said pump is reversible for effecting both            de-priming and priming operations.            Optionally, a check valve is positioned between said ink            reservoir and said ink chamber for isolating said ink            reservoir from said printhead during a priming operation.            Optionally, said float valve comprises:    -   an arm pivotally mounted about a pivot;    -   a float mounted at one end of said arm; and    -   a valve head mounted at an opposite end of said arm,        wherein said valve head is positioned for sealing engagement        with a valve seat at said inlet port.        Optionally, said ink chamber is a pressure-regulating chamber        for regulating a hydrostatic pressure of ink supplied to said        printhead during normal printing.        Optionally, said printhead is a replaceable pagewidth printhead.        Optionally, said printhead comprises one or more printhead        integrated circuits mounted on an ink distribution manifold,        each printhead integrated circuit comprising a plurality of        nozzles, and said manifold having said ink inlet and an ink        outlet connected to a downstream ink line.        In an eighth aspect the present invention provides a printer        comprising:    -   an inkjet printhead having an ink inlet, an ink outlet and a        plurality of nozzles;    -   an ink chamber having an outlet port;    -   an upstream ink line providing fluid communication between said        outlet port and said ink inlet;    -   a reversible air pump having a pump outlet communicating with a        headspace in said ink chamber, said pump being configured to        positively pressurize said headspace during a printhead priming        operation or negatively pressurize said headspace during a        printhead depriming operation; and    -   a downstream ink line connected to said ink outlet, said        downstream ink line being in fluid communication with a pump        inlet so as to effect cooperative pulling and pushing of ink        through said printhead during said priming and depriming        operations.        In a further aspect there is provided a printer further        comprising an ink reservoir positioned above said ink chamber        and in fluid communication with an inlet port of said ink        chamber.        Optionally, said ink reservoir is isolable from said ink chamber        during both priming and depriming operations.        Optionally, said ink reservoir comprises a check valve        configured to isolate said ink reservoir from said ink chamber        when said headspace is positively pressurized during said        printhead priming operation.        Optionally, said ink chamber comprises a float valve configured        to isolate said ink reservoir from said ink chamber when said        headspace is negatively pressurized during said printhead        depriming operation.        Optionally, said float valve comprises:    -   an arm pivotally mounted about a pivot;    -   a float mounted at one end of said arm; and    -   a valve head mounted at an opposite end of said arm,        wherein said valve head is positioned for sealing engagement        with a valve seat at said inlet port.        Optionally, said ink chamber is a pressure-regulating chamber        for regulating a hydrostatic pressure of ink supplied to said        printhead during normal printing.        Optionally, said pressure-regulating chamber is positioned below        said printhead so as to provide a negative hydrostatic pressure.        Optionally, said printhead is a replaceable pagewidth printhead.        Optionally, said printhead comprises one or more printhead        integrated circuits mounted on an ink distribution manifold,        each printhead integrated circuit comprising a plurality of        nozzles, and said manifold having said ink inlet and said ink        outlet.        In a further aspect there is provided a printer further        comprising means for controlling a flow of ink from said        downstream ink line back into said ink chamber when said        printhead is primed.        Optionally, said means is selected from the group comprising:    -   an electronically-controlled valve;    -   a check-valve; and    -   a loop section passing below said level of ink in said chamber.        In a further aspect there is provided a printer further        comprising a sensor positioned for sensing ink in said        downstream ink line, said sensor cooperating with said pump such        that said pump is shut off when said sensor senses any ink.        Optionally, said sensor comprises an optical sensor.        In a further aspect there is provided a printer further        comprising means for minimizing phantom sensing of ink caused by        ink bubbles in said downstream ink line.        In another aspect there is provided a printer comprising a        bubble-bursting box, said box comprising:    -   one or more bubble-bursting chambers having a respective chamber        inlet connected to said downstream ink line; and    -   an air outlet in fluid communication with said pump inlet.        Optionally, said sensor is positioned to sense ink above a        bubble-bursting point in at least one of said bubble-bursting        chambers.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of said ink supply system.        Optionally, each bubble-bursting chamber is dimensioned to        promote expansion and bursting of ink bubbles entering said        chamber via said chamber inlet.        Optionally, said bubble-bursting box comprises a common air        chamber in fluid communication with said bubble-bursting        chambers via an air channel defined in a roof of said box, said        air outlet being defined in a base of said air chamber.        In a ninth aspect the present invention provided a method of        priming a printhead whilst minimizing nozzle drooling, said        method comprising the steps of:    -   (i) providing a printhead comprising:        -   an ink distribution manifold having an ink inlet and an ink            outlet; and        -   one or more printhead integrated circuits mounted on said            manifold, each printhead integrated circuit comprising a            plurality of nozzles;    -   (ii) providing an ink chamber in fluid communication with said        ink inlet; and    -   (iii) applying a positive pressure at said ink inlet whilst        simultaneously applying a negative pressure at said ink outlet        so as to draw ink through said manifold and prime said printhead        whilst minimizing nozzle drooling.        Optionally, said printhead is a pagewidth inkjet printhead.        Optionally, said positive pressure is applied by positively        pressurizing a headspace above ink in said ink chamber.        Optionally, said positive pressure is applied using a pump        having a pump outlet communicating with said headspace.        Optionally, a pump inlet communicates with said ink outlet so as        to apply said negative pressure at said ink outlet.        Optionally, a downstream ink line is connected to said ink        outlet, and said method further comprises the steps of:    -   monitoring for the presence of ink in said downstream ink line;        and    -   shutting off said pump when ink is sensed in said downstream ink        line.        Optionally, an optical sensor is provided for sensing said ink        in said downstream ink line.        Optionally, phantom sensing of ink caused by ink bubbles in said        downstream ink line is minimized.        Optionally, phantom sensing of ink is minimized by sensing for        ink above a bubble-bursting point in a bubble-bursting chamber        provided in said downstream ink line.        Optionally, said bubble-bursting chamber is in fluid        communication with an air outlet, said air outlet being in fluid        communication with a pump inlet.        In a tenth aspect the present invention provides a method of        priming one or more printhead integrated circuits, said method        comprising the steps of:    -   (i) providing a printhead assembly comprising:        -   an ink distribution manifold having an ink inlet and an ink            outlet;        -   one or more printhead integrated circuits mounted on said            manifold, each printhead integrated circuit comprising a            plurality of nozzles;        -   an upstream ink line connected to said ink inlet; and        -   a downstream ink line connected to said ink outlet, wherein            at least part of said printhead assembly contains ink            bubbles;    -   (ii) providing an ink chamber in fluid communication with said        ink inlet via said upstream ink line;    -   (iii) priming said printhead integrated circuits by drawing ink        from said ink chamber, through said manifold and into said        downstream ink line using a pump;    -   (iv) bursting ink bubbles in said downstream ink line;    -   (v) sensing for ink downstream of a bubble-bursting point in        said downstream ink line; and    -   (v) shutting off said pump when said ink is sensed.        Optionally, said printhead is a pagewidth inkjet printhead.        Optionally, said priming is performed by positively pressurizing        a headspace above ink in said ink chamber.        Optionally, a pump outlet of said pump communicates with said        headspace.        Optionally, a pump inlet communicates with said ink outlet so as        to apply negative pressure simultaneously at said ink outlet.        Optionally, a loop in said downstream ink conduit prevents ink        from flowing back into said ink chamber when said pump is shut        off, said loop passing below a level of ink in said ink chamber.        Optionally, a valve in said downstream ink conduit prevents ink        from flowing back into said ink chamber when said pump is shut        off        Optionally, said bubbles are burst by expansion of said bubbles.        Optionally, said bubbles are burst using a bubble-bursting box        provided in said downstream ink line, said bubble-bursting box        comprising:    -   a bubble-bursting chamber having a respective chamber inlet        defined in a base thereof, said chamber inlet being connected to        a downstream ink conduit; and    -   an air outlet in fluid communication said chamber.        Optionally, an optical sensor is positioned above a        bubble-bursting point in said bubble-bursting chamber.        Optionally, said bubble-bursting chamber is dimensioned to        promote expansion and bursting of ink bubbles entering said        chamber via said chamber inlet.        Optionally, each bubble-bursting chamber has curved sidewalls,        wherein a curvature of said sidewalls is greater than a        curvature of said downstream ink conduit.        Optionally, each bubble-bursting chamber is generally        crescent-shaped, thereby maximizing said curvature in a minimal        volume.        Optionally, said bubble-bursting box comprises an air chamber in        fluid communication with said bubble-bursting chamber, said air        outlet being positioned in said air chamber.        Optionally, each bubble-bursting chamber communicates with said        air chamber via a respective air channel defined in a roof of        said box.        Optionally, each air channel is a hydrophobic serpentine channel        for minimizing transfer of ink to said air chamber when said box        is tipped.        Optionally, each air channel comprises at least one ink-trapping        stomach.        Optionally, each air channel terminates at a channel outlet        defined in a roof of said box, each channel outlet being        positioned to deposit ink into said air chamber.        Optionally, said air outlet is defined in a base of said air        chamber, and each channel outlet is offset from said air outlet.        In an eleventh aspect the present invention provides a method of        replacing a printhead in an inkjet printer with minimal ink        wastage, said method comprising the steps of:    -   (i) providing a printhead comprising:        -   an ink distribution manifold having an ink inlet and an ink            outlet;        -   one or more printhead integrated circuits mounted on said            manifold, each printhead integrated circuit comprising a            plurality of nozzles;    -   (ii) providing an ink supply system comprising:        -   an ink chamber in fluid communication with said ink inlet            via an upstream ink line;        -   a reversible air pump communicating with a headspace of said            ink chamber; and        -   a downstream ink line connected to said ink outlet;    -   (ii) actuating said pump so as to negatively pressurize said        headspace, thereby depriming said printhead by drawing ink from        said downstream ink line and said printhead into said ink        chamber;    -   (iii) deactuating said pump and allowing an ink level in said        ink chamber to equalize with an ink level in said upstream ink        line;    -   (iv) removing said printhead from said printer, said removing        including disconnecting said ink inlet and said ink outlet from        respective upstream and downstream ink lines;    -   (v) replacing said printhead with a replacement printhead, said        replacing including connecting an ink inlet and an outlet inlet        of said replacement printhead with respective upstream and        downstream ink lines;    -   (vi) actuating said pump so as to positively pressurize said        headspace, thereby priming said printhead by drawing ink from        said ink chamber, through said printhead and into said        downstream ink line; and    -   (vii) deactuating said pump and allowing an ink level in said        ink chamber to equilibrate to a predetermined level.        Optionally, said ink chamber has sufficient capacity to        accommodate ink drawn into said chamber during said depriming        step.        Optionally, said downstream ink line comprises a loop section        passing below a level of ink in said ink chamber, wherein said        predetermined ink level in said ink chamber equalizes with an        ink level in said loop section after deactuation of said pump in        step (vii).        Optionally, said downstream ink line comprises an inline        electronically-operated valve.        In another aspect the method further comprising the steps of:    -   sensing ink in said downstream ink line using a sensor; and    -   deactuating said pump in response to sensing ink in said        downstream ink line.        Optionally, phantom sensing of ink caused by ink bubbles in said        downstream ink line is minimized.        Optionally, phantom sensing of ink is minimized by sensing for        ink above a bubble-bursting point in a bubble-bursting chamber        provided in said downstream ink line.        Optionally, said ink chamber is a pressure-regulating chamber        for controlling a hydrostatic pressure of ink supplied to said        printhead during normal printing.        Optionally, said pressure-regulating chamber comprises a float        valve for maintaining a predetermined level of ink in said        chamber, said float valve controlling a supply of ink to said        chamber by an ink reservoir in fluid communication therewith.        In another aspect there is provided a method further comprising        the step of:    -   printing from said replacement printhead whilst controlling said        hydrostatic pressure of ink using said pressure-regulating        chamber.        Optionally, said float valve isolates said chamber from said ink        reservoir during said depriming in step (ii).        Optionally, said ink reservoir comprises a check valve, said        check valve isolating said chamber from said ink reservoir        during said priming in step (vi).        In a twelfth aspect the present invention provides a printer        comprising:    -   a printhead having an ink inlet and an ink outlet;    -   a pressure-regulating chamber having an outlet port connected to        said ink inlet via an upstream ink conduit, said chamber        containing ink at a first level below said printhead,        wherein a headspace above said first level of ink is open to        atmosphere; and    -   a downstream ink conduit connected to said ink outlet and        terminating above said first level of ink, said downstream ink        conduit being open to atmosphere,        wherein said downstream ink conduit comprises a loop section        passing below said first level of ink, such that, in a printing        configuration, a second level of ink in said loop is equal to        said first level of ink in said chamber.        In a further aspect the printer comprising means for maintaining        a predetermined first level of ink in said chamber, said        predetermined first level of ink controlling a hydrostatic        pressure of ink supplied to said ink inlet.        Optionally, said hydrostatic pressure, relative to atmospheric        pressure, is defined as ρgh, wherein ρ is the density of ink, g        is acceleration due to gravity and h is the height of the        predetermined first level of ink relative to the printhead.        Optionally, said means for maintaining said predetermined first        level of ink comprises an ink reservoir cooperating with a float        valve contained in said pressure-regulating chamber.        Optionally, said float valve comprises:    -   an arm pivotally mounted about a pivot;    -   a float mounted at one end of said arm; and    -   a valve head mounted at an opposite end of said arm,        wherein said valve head is positioned for sealing engagement        with a valve seat at an inlet port of said pressure-regulating        chamber.        Optionally, said inlet port and said outlet port of said        pressure-regulating chamber are positioned towards a base of        said chamber.        In a further aspect the printer further comprising a printhead        priming system.        In another aspect the printer comprising:    -   an air pump communicating with said headspace above said ink in        said chamber; and    -   a valve positioned between said ink reservoir and said inlet        port,        wherein, in a priming configuration, said valve is configured to        be shut and said pump is configured to positively pressurize        said headspace thereby forcing ink from said chamber into said        downstream ink conduit.        Optionally, a sensor is positioned for sensing ink towards a        terminus of said downstream ink conduit, said sensor cooperating        with said pump such that said pump is shut off when said sensor        senses any ink.        Optionally, said loop section controls an amount of ink flowing        from said downstream ink line back into said pressure-regulating        chamber so as to restore said printing configuration after        priming.        Optionally, said sensor is an optical sensor.        In another aspect the printer further comprising means for        minimizing phantom sensing of ink caused by ink bubbles in said        downstream ink line.        In a further aspect the printer comprising a bubble-bursting        box, said box comprising:    -   at least one bubble-bursting chamber having a respective chamber        inlet; and    -   an air outlet.        Optionally, said air outlet is open to atmosphere or said air        outlet communicates with a pump inlet of said air pump.        Optionally, said at least one bubble-bursting chamber is        dimensioned to promote expansion and bursting of ink bubbles        entering said chamber via said chamber inlet.        Optionally, said bubble-bursting box comprises a plurality of        bubble-bursting chambers, each chamber corresponding to a        respective ink channel of said printer.        Optionally, said bubble-bursting box comprises an air chamber in        fluid communication with said at least one bubble-bursting        chamber via an air channel defined in a roof of said box, said        air outlet being defined in said air chamber.        Optionally, said air channel is a hydrophobic serpentine channel        comprising at least one ink-trapping stomach, said air channel        minimizing transfer of ink to said air chamber when said box is        tipped.        Optionally, said pump is a reversible pump.        Optionally, in a de-priming configuration, said pump is reversed        and ink is pulled from said printhead towards said        pressure-regulating chamber.        In a thirteenth aspect the present invention provides a printer        comprising:    -   an inkjet printhead having a plurality of ink inlets, a        plurality of ink outlets and an array of nozzles;    -   a plurality of ink chambers, each ink chamber having an outlet        port connected to a corresponding ink inlet via a respective        upstream ink conduit;    -   a single air pump having a pump outlet communicating with a        headspace in each ink chamber, said pump being configured to        positively pressurize each headspace during a printhead priming        operation; and    -   a plurality of downstream ink conduits, each downstream ink        conduit being connected to a corresponding ink outlet, and each        downstream ink conduit communicating with a pump inlet of said        pump.        In another aspect the printer further comprising means for        inhibiting ink in said downstream ink conduits from reaching        said pump inlet.        Optionally, said means includes an expansion box, said expansion        box comprising:    -   a plurality of expansion chambers, each expansion chamber having        a respective chamber inlet defined in a base thereof, each        chamber inlet being connected to a respective downstream ink        conduit;    -   a common air chamber having an air outlet defined in a base        thereof, said air outlet being connected to said pump inlet via        a pump inlet conduit; and    -   a cover for said expansion chambers and said common air chamber,        said cover defining a roof of said box, said cover having a        plurality of air channels defined therein, each air channel        providing fluid communication between a respective expansion        chamber and said common air chamber.        Optionally, each air channel is a serpentine channel for        minimizing transfer of ink from said expansion chambers to said        common air chamber.        Optionally, each air channel is hydrophobic.        Optionally, each air channel comprises at least one ink-trapping        stomach.        Optionally, each air channel terminates at a channel outlet        defined in a roof of said air chamber, each channel outlet being        positioned to deposit ink into said air chamber.        Optionally, each channel outlet is offset from said air outlet.        Optionally, a snorkel extends from said air outlet towards said        roof, thereby maximizing an effective ink-collecting volume of        said air chamber.        Optionally, said air chamber has an air vent defined therein.        Optionally, said air chamber has one or more air vents defined        therein, the number of air vents regulating a pressure in said        ink expansion box.        Optionally, said means further comprises a timing circuit for        controlling operation of said pump during printhead priming.        Optionally, said means further comprises an ink sensor for        sensing ink in at least one of said expansion chambers, said        sensor cooperating with said pump such that said pump is shut        off when said sensor senses ink.        Optionally, said expansion chambers are configured to promote        expansion and bursting of ink bubbles entering said chambers via        said chamber inlets, thereby minimizing phantom sensing of ink        in said at least one chamber.        Optionally, said air pump is reversible for effecting both        priming and depriming operations.        In another aspect there is provided a printer further comprising        a conduit junction, said conduit junction comprising:    -   a plurality of junction outlets, each junction outlet being        connected to a headspace port of each ink chamber;    -   a junction inlet connected to said pump outlet.        Optionally, said conduit junction comprises an air vent such        that each headspace is open to atmosphere.        Optionally, said downstream ink conduit comprises any one of:    -   an inline electronically-controlled valve; and    -   a loop section passing below a level of ink in said ink chamber.        Optionally, said ink chamber maintains a predetermined level of        ink when said pump is switched off.        Optionally, said ink chamber comprises a float valve cooperating        with an ink reservoir for maintaining said predetermined level        of ink.        In a fourteenth aspect the present invention provided a printer        comprising:    -   an inkjet printhead having an ink inlet, an ink outlet and an        array of nozzles;    -   an ink chamber having an outlet port connected to said ink inlet        via an upstream ink conduit;    -   an air pump having a pump outlet communicating with a headspace        in said ink chamber, said pump being configured to positively        pressurize said headspace during a printhead priming operation;        and    -   a downstream ink conduit connected to said ink outlet, said        downstream ink conduit communicating with a pump inlet of said        pump,        wherein said downstream ink conduit includes an expansion        chamber for accommodating a volume of ink, thereby inhibiting        said ink from reaching said pump inlet.        Optionally, said expansion chamber is in fluid communication        with an air chamber, said air chamber having an air outlet        connected to said pump inlet.        Optionally, said expansion chamber is part of an expansion box,        said expansion box comprising:    -   at least one expansion chamber, said expansion chamber having a        respective chamber inlet defined in a base thereof, said chamber        inlet being connected to said downstream ink conduit;    -   a common air chamber having an air outlet defined in a base        thereof, said air outlet being connected to said pump inlet via        a pump inlet conduit; and    -   a cover for said expansion chamber and said common air chamber,        said cover defining a roof of said box, said cover having at        least one air channel defined therein, said air channel        providing fluid communication between said at least one        expansion chamber and said common air chamber.        Optionally, said air channel is a serpentine channel for        minimizing transfer of ink from said expansion chamber to said        common air chamber.        Optionally, said air channel is hydrophobic.        Optionally, said air channel comprises at least one ink-trapping        stomach.        Optionally, said air channel terminates at a channel outlet        defined in a roof of said air chamber, said channel outlet being        positioned to deposit ink into said air chamber.        Optionally, said channel outlet is offset from said air outlet.        Optionally, a snorkel extends from said air outlet towards said        roof, thereby maximizing an effective ink-collecting volume of        said air chamber.        Optionally, said air chamber has an air vent defined therein.        Optionally, said air chamber has one or more air vents defined        therein, the number of air vents regulating a pressure in said        expansion box.        In a further aspect there is provided a printer comprising a        timing circuit for controlling operation of said pump during        printhead priming.        In another aspect there is provided a printer comprising an ink        sensor for sensing ink in said expansion chamber, said sensor        cooperating with said pump such that said pump is shut off when        said sensor senses ink.        Optionally, said expansion chamber is configured to promote        expansion and bursting of ink bubbles entering said chamber,        thereby minimizing phantom sensing of ink in said chamber.        Optionally, said air pump is reversible for effecting both        priming and depriming operations.        In a further aspect there is provided a printer further        comprising a conduit junction, said conduit junction comprising:    -   a plurality of junction outlets, each junction outlet being        connected to a headspace port of each ink chamber;    -   a junction inlet connected to said pump outlet.        Optionally, said conduit junction comprises an air vent such        that each headspace is open to atmosphere.        Optionally, said downstream ink conduit comprises any one of:    -   an inline electronically-controlled valve; and    -   a loop section passing below a level of ink in said ink chamber.        Optionally, said ink chamber maintains a predetermined level of        ink when said pump is switched off.        Optionally, said ink chamber comprises a float valve cooperating        with an ink reservoir for maintaining said predetermined level        of ink.        In a fifteenth aspect the present invention provided a method of        priming one or more inkjet printheads, said method comprising        the steps of:    -   (i) providing a printhead assembly comprising:        -   an ink distribution manifold having an ink inlet and an ink            outlet;        -   one or more inkjet printheads mounted on said manifold, each            inkjet printhead comprising an array of nozzles;        -   an upstream ink line connected to said ink inlet; and        -   a downstream ink line connected to said ink outlet;    -   (ii) providing an ink chamber in fluid communication with said        ink inlet via said upstream ink line;    -   (iii) providing an air pump having a pump outlet in fluid        communication with a headspace of said ink chamber, and a pump        inlet in fluid communication with said downstream ink line;    -   (iii) actuating said air pump so as to draw ink from said ink        chamber, through said manifold and into said downstream ink        line, thereby priming said inkjet printheads;    -   (iv) receiving said ink in an expansion chamber in said        downstream ink line; and    -   (v) deactuating said pump.        Optionally, said downstream ink line comprises a loop section        passing below a level of ink in said ink chamber, wherein an ink        level in said loop section equalizes with an ink level in said        ink chamber after deactuation of said pump in step (v).        Optionally, said downstream ink line comprises an inline        electronically-operated valve.        In another aspect the method further comprising the steps of:    -   sensing ink in said downstream ink line using a sensor; and    -   deactuating said pump in response to sensing ink in said        downstream ink line.        Optionally, phantom sensing of ink caused by ink bubbles in said        downstream ink line is minimized.        Optionally, phantom sensing of ink is minimized by sensing for        ink above a bubble-bursting point in a bubble-bursting chamber        provided in said downstream ink line.        Optionally, said ink chamber is a pressure-regulating chamber        for controlling a hydrostatic pressure of ink supplied to said        printhead during normal printing.        Optionally, said pressure-regulating chamber comprises a float        valve for maintaining a predetermined level of ink in said        chamber, said float valve controlling a supply of ink to said        chamber by an ink reservoir in fluid communication therewith.        In a further aspect there is provided a method further        comprising the step of:    -   printing from said replacement printhead whilst controlling said        hydrostatic pressure of ink using said pressure-regulating        chamber.        Optionally, said ink reservoir comprises a check valve, said        check valve isolating said ink chamber from said ink reservoir        during said priming in step (iii).        Optionally, said expansion chamber is part of an expansion box,        said expansion box comprising:    -   at least one expansion chamber, said expansion chamber having a        respective chamber inlet defined in a base thereof, said chamber        inlet being connected to said downstream ink conduit;    -   a common air chamber having an air outlet defined in a base        thereof, said air outlet being connected to said pump inlet via        a pump inlet conduit; and    -   a cover for said expansion chamber and said common air chamber,        said cover defining a roof of said box, said cover having at        least one air channel defined therein, said air channel        providing fluid communication between said at least one        expansion chamber and said common air chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a printhead cartridge installed in a print engine of aprinter;

FIG. 2 shows the print engine without the printhead cartridge installedto expose inlet and outlet ink manifolds;

FIG. 3 is a perspective of the complete printhead cartridge;

FIG. 4 shows the printhead cartridge of FIG. 3 with the protective coverremoved;

FIG. 5 is an exploded perspective of the printhead cartridge shown inFIG. 3;

FIG. 6 is an exploded perspective of a printhead, which forms part ofthe printhead cartridge shown in FIG. 3;

FIG. 7 is a schematic of the fluidics system according to the presentinvention, configured for normal printing;

FIG. 8 shows the fluidics system of FIG. 7 in a configuration ready forprinthead priming;

FIG. 9 shows the fluidics system of FIG. 7 configured for printheadpriming;

FIG. 10 shows the fluidics system of FIG. 7 after printhead printheadpriming;

FIG. 11 shows an alternative fluidics system according to the presentinvention;

FIG. 12 shows the fluidics system of FIG. 7 configured for printheaddepriming;

FIG. 13 shows the fluidics system of FIG. 7 in a deprimed configurationwith the printhead removed;

FIG. 14 shows the fluidics system of FIG. 13 with a new printheadinstalled and primed;

FIG. 15 is an exploded top perspective of a bubble-bursting boxaccording to the present invention;

FIG. 16 is an exploded bottom perspective of the bubble-bursting boxshown in FIG. 15;

FIG. 17 is a perspective of the assembled bubble-bursting box shown inFIG. 15;

FIG. 18 is an exploded perspective of a pressure-regulating chamber;

FIG. 19 is a perspective of the print engine shown in FIG. 1 withfluidics components; and

FIG. 20 shows fluidic connections for a five channel ink supply systemaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Print Engine andPrinthead Cartridge Overview

FIG. 1 shows a printhead cartridge 2 installed in a print engine 3. Theprint engine 3 is the mechanical heart of a printer which can have manydifferent external casing shapes, ink tank locations and capacities, aswell as media feed and collection trays. The printhead cartridge 2 canbe inserted in and removed from the print engine 3 enabling periodicreplacement. To remove the printhead cartridge 2, a user lifts a latch27 and lifts the cartridge out from the print engine 3. FIG. 2 shows theprint engine 3 with the printhead cartridge 2 removed.

When inserting the printhead cartridge 2 into the print engine 3,electrical and fluidic connections are made between the cartridge andthe print engine. Contacts 33 on the printhead cartridge 2 (see FIG. 4)engage with complementary contacts (not shown) on the print engine 3. Inaddition, an ink inlet manifold 48 and an ink outlet manifold 50 on theprinthead cartridge 2 mate with complementary sockets 20 on the printengine 3. The ink inlet manifold 48 provides a plurality of ink inletsfor the printhead cartridge 2, each corresponding to a different colorchannel. Likewise, the ink outlet manifold 50 provides a plurality ofink outlets for the printhead cartridge 2, each corresponding to adifferent color channel. As will be explained in more detail below, thefluidics system of the present invention typically requires ink to flowthrough the printhead cartridge 2, from an ink inlet to an ink outlet,in order to achieve priming and depriming of the printhead.

Referring again to FIG. 2, with the printhead cartridge 2 removed,apertures 22 are revealed in each of the sockets 20. Each aperture 22receives a complementary spout 52 and 54 on the inlet and outletmanifolds 48 and 50, respectively (see FIG. 5).

Ink is supplied to a rear of an inlet socket 20B frompressure-regulating chambers 106, which are usually mounted towards abase of the print engine 3 (see FIG. 19). The pressure-regulatingchambers receive ink by gravity from ink tanks 128 mounted elsewhere onthe print engine 3.

Ink exits from a rear of an outlet socket 20A, which is connected viaconduits to a bubble-bursting box (not shown in FIG. 2). Details of thefluidic system and its components will be described in greater detailbelow.

FIG. 3 is a perspective of the complete printhead cartridge 2 removedfrom the print engine 3. The printhead cartridge 2 has a top molding 44and a removable protective cover 42. The top molding 44 has a centralweb for structural stiffness and to provide textured grip surfaces 58for manipulating the cartridge during insertion and removal. A baseportion of the protective cover 42 protects printhead ICs 30 and theline of contacts 33 (see FIG. 4) prior to installation in the printer.Caps 56 are integrally formed with the base portion and cover ink inletspouts 52 and outlet spouts 54 (see FIG. 5).

FIG. 4 shows the printhead cartridge 2 with its protective cover 42removed to expose printhead ICs (not shown in FIG. 4) on a bottomsurface and the line of contacts 33 on a side surface of the printheadcartridge. The protective cover 42 may be either discarded or fitted toa printhead cartridge being replaced so as to contain any leakage fromresidual ink.

FIG. 5 is partially exploded perspective of the printhead cartridge 2.The top cover molding 44 has been removed to reveal the inlet manifold48 and the outlet manifold 50. Inlet and outlet shrouds 46 and 47 havealso been removed to expose the five inlet spouts 52 and five outletspouts 54. The inlet and outlet spouts 52 and 54 connect withcorresponding ink inlets 60 and ink outlets 61 in an LCP cavity molding72 attached to the inlet and outlet manifolds 48 and 50. The ink inlets60 and ink outlets 61 are each in fluid communication with correspondingmain channels 24 in an LCP channel molding 68 (see FIG. 6).

Referring now to FIG. 6, the five main channels 24 extend the length ofthe LCP channel molding 68 and feed into a series of fine channels (notshown) on the underside of the LCP molding 68. The LCP cavity molding72, having a plurality of air cavities 26 defined therein, mates with atopside of the LCP channel molding 68 such that the air cavitiesfluidically communicate with the main channels 24. The air cavities 26serve to dampen shock waves or pressure pulses in ink being suppliedalong the main channels 24 by compressing air in the cavities.

A die attach film 66 has one surface bonded to an underside of the LCPchannel molding 68 and an opposite surface bonded to a plurality ofprinthead ICs 30. A plurality of laser-ablated holes 67 in the film 66provide fluidic communication between the printhead ICs 30 and the mainchannels 24. Further details of the arrangement of the printhead ICs 30,the film 66 and the LCP channel molding 68 can be found in the USPublication No. 2007/0206056, the contents of which is incorporatedherein by reference. Further details of the inlet manifold 48 and outletmanifold 50 can be found in, for example, U.S. application Ser. No.12/014,769 filed Jan. 16, 2008, the contents of which is incorporatedherein by reference.

Electrical connections to the printhead ICs 30 are provided by a flexPCB 70 which wraps around the LCP moldings 72 and 68, and connects withwirebonds 64 extending from bond pads (not shown) on each printhead IC30. The wirebonds 64 are protected with wirebond protector 62. Asdescribed above, the flex PCB 70 includes the contacts 33, which connectwith complementary contacts in the print engine 3 when the printheadcartridge 2 is installed for use.

Fluidics System

From the foregoing, it will be appreciated that the printhead cartridge2 has a plurality of ink inlets 60 and ink outlets 61, which can feedink through main channels 24 in the LCP channel molding 68 to whichprinthead ICs 30 are attached. The fluidics system, which supplies inkto and from the printhead, will now be described in detail. For theavoidance of doubt, a “printhead” may comprise, for example, the LCPchannel molding 68 together with the printhead ICs 30 attached thereto.Thus, any printhead assembly with at least one ink inlet and at leastone ink outlet may be termed “printhead” herein.

Referring to FIG. 7, there is shown schematically a fluidic system 100in accordance with the present invention. Relative positioning of eachcomponent of the system 100 will be described herein with reference tothe schematic drawings. However, it will be appreciated that the exactpositioning of each component in the print engine 3 will be a matter ofdesign choice of the person skilled in the art.

For simplicity, the fluidics system 100 is shown for one color channel.Single color channel printheads are, of course, within the ambit of thepresent invention. However, the fluidics system 100 is more usually usedin connection with a full color inkjet printhead having a plurality ofcolor channels (e.g. five color channels as shown in FIGS. 5 and 6).Whilst the following discussion generally relates to one color channel,the skilled person will readily appreciate that multiple color channelsmay use corresponding fluidics systems. Indeed, a multi color channelfluidics system is shown in FIG. 20.

Normal Printing

As shown in FIG. 7, the system 100 is configured in a normal printingmode—that is, a printhead 102 is primed with ink and a hydrostaticpressure of ink 104 supplied to the printhead is regulated. Typically,during normal printing, it is necessary to maintain a constanthydrostatic ink pressure, which is negative relative to atmosphericpressure. A negative hydrostatic ink pressure is necessary to preventprinthead face flooding when printing ceases. Indeed, most commerciallyavailable inkjet printers operate at negative hydrostatic ink pressures,which is usually achieved through the use of a capillary foam in an inktank.

In the fluidic system 100, a pressure-regulating chamber 106 suppliesink 104 to an ink inlet 108 of the printhead. The pressure-regulatingchamber 106 is positioned below the printhead 102 and maintains apredetermined set level 110 of ink therein. The height of the printhead102 above this set level 110 controls the hydrostatic pressure of ink104 supplied to the printhead. The actual hydrostatic pressure isgoverned by the well-known equation: p=ρgh, where p is the hydrostaticink pressure, ρ is the ink density, g is acceleration due to gravity andh is the height of the set level 110 of ink relative to the printhead102. The printhead 102 is typically positioned at a height of about 10to 300 mm above the set level 110 of ink, optionally about 50 to 200 mm,optionally about 80 to 150 mm, or optionally about 90 to 120 mm abovethe set level.

Gravity provides a very reliable and stable means for controlling thehydrostatic ink pressure. Provided that the set level 110 remainsconstant, then the hydrostatic ink pressure will also remain constant.

The pressure-regulating chamber 106 comprises a float valve formaintaining the set level 110 during normal printing. The float valvecomprises an arm 112, which is pivotally mounted about a pivot 114. Afloat 116 is mounted at one end of the arm 112, and a valve head in theform of a poppet 118 is attached to an opposite end of the arm. Thevalve poppet 118 is slidably received in a valve guide 120 and sealinglyengages with a valve seat 122 positioned in an inlet port 124 of thepressure-regulating chamber 106. The inlet port 124 is positionedtowards a base of the chamber 106.

The set level 110 is determined by the buoyancy of the float 116 in theink 104 (as well as the position of the chamber 106 relative to theprinthead 102). The poppet valve 118 should seal against the seat 122 atthe set level 110, but should unseal upon any downward movement of thefloat 116. Preferably, there should be minimum hysteresis in the floatvalve so as to minimize variations in hydrostatic pressure. Thehysteresis of the float valve should preferably be about ±2 mm or less.Potential sources of hysteresis include pivot friction, valve guidefriction, sticking between the compliant poppet valve and the valveseat, and looseness in the lever arm to poppet valve linkage.

From FIG. 7, it will be seen that as ink 104 is drawn from an outletport 126 of the chamber 106 during normal printing, the float 116incrementally moves downwards, which opens the inlet port 124 and allowsink to refill the chamber from an ink reservoir 128. In this way, theset level 110 is maintained and the hydrostatic ink pressure in theprinthead 102 remains constant.

The float 116 preferably occupies most of the volume of the chamber 106so as to provide maximum valve closure force. This closure force isamplified by the lever arm 112. However, the float 116 should beconfigured so that it does not touch sidewalls of the chamber 106 so asto avoid sticking.

Ink 104 is supplied to the pressure-regulating chamber 106 by the inkreservoir 128 positioned at any height above the set level 110. The inkreservoir 128 is typically a user-replaceable ink tank or ink cartridge,which connects with a supply conduit 130 when installed in the printer.The supply conduit 130 provides fluidic communication between the inkreservoir 128 and the inlet port 124 of the pressure-regulating chamber106.

The ink reservoir 128 vents to atmosphere via a first air vent 132,which opens into a headspace of the ink reservoir. Accordingly, the ink104 can simply drain into the pressure-regulating chamber 106 when thefloat valve opens the inlet port 124. The vent 132 comprises ahydrophobic serpentine channel 135, which minimizes ink losses throughthe vent when the ink cartridge is tipped. The vent 132 may also beprotected by a one-time use sealing strip (not shown), which is removedprior to installation of an ink cartridge in the printer.

The printhead 102 has an ink inlet 108, which connects to the outletport 126 via an upstream ink conduit 134. It will be understood thatpressure-regulation as described above may be achieved with printheadshaving an ink inlet, but no ink outlet.

However, for the purposes of priming (described below), the printhead102 shown in FIGS. 7 to 13 also has an ink outlet 136, which isconnected to a downstream ink conduit 138. The downstream ink conduit138 has a loop section 180, which loops below the set level 110 and thenrises back up above the height of the set level and the printhead 102.Ink 104 in the upstream ink conduit 134 and pressure-regulating chamber150 is open to atmosphere via a second air vent 150 in communicationwith the headspace 139. Likewise, ink in the downstream ink conduit 138is open to atmosphere via a third air vent 163. The loop 180 in thedownstream ink conduit 138 ensures that ink at the outlet 136 of theprinthead 102 is at the same hydrostatic pressure as ink at the inlet108. This is because ink in the downstream ink conduit 138 is held inthe loop 180 at the set level 110 by virtue of both the upstream anddownstream conduits being open to atmosphere, thereby allowingequilibration in the loop 180 to the set level.

Of course, the loop 180 may alternatively be replaced with, for example,an electronically-controlled valve (see valve 172 in FIG. 11), which canisolate the ink outlet 136 from atmosphere so that the printhead 106effectively has no ink outlet during normal printing. However, the loop180 provides a simple means of controlling hydrostatic pressure at theink outlet 136 without the need for a complex electronically-operatedvalve.

Printhead Priming

Printhead priming requires ink 104 to be fed into the ink inlet 108 ofthe printhead 102 via an upstream ink conduit 134 interconnecting theink inlet and the outlet port 126 of the pressure-regulating chamber106. In order to provide optimum control of both priming and depriming,ink is fed through the printhead 102 and exits via the ink outlet 136which is connected to the downstream ink conduit 138. Once the ink 104is fed through the main channels 24 in the LCP channel molding 68, theprinthead ICs 30 are primed by capillary action.

In principle, the ink 104 may be fed through the printhead 102 either bypositively pressurizing an inlet side of the printhead, or by negativelypressurizing an outlet side of the printhead. However, a number ofproblems exist depending on whether the printhead to be primed is wet(e.g. containing ink bubbles) or dry. A dry pagewidth printhead primesadequately when about 1 kPa of positive pressure is applied to the inkinlet side of the printhead. At this priming pressure, no undesirable‘drooling’ of ink from printhead nozzles is observed. However, if theprinthead is wet and contains residual ink bubbles, then the requisitepositive priming pressure increases to about 3 kPa. At this higherpriming pressure, drooling of ink from nozzles is observed, whichrequires removal by printhead maintenance.

The drooling phenomenon in a wet printhead can be mitigated by primingusing a negative pressure applied at the ink outlet 136. However, if adry printhead is primed using a negative pressure, then excessive airingestion through the printhead nozzles causes the ink to foam, which isalso undesirable. Since wet and dry printhead have different optimumpriming conditions, there is a need to provide a priming system whichcan adequately prime a printhead in either state.

FIG. 8 shows the fluidics system 100 in a state ready for priming a dry,unprimed printhead 102. A priming sub-system of the fluidics system 100will now be discussed in detail with reference to FIGS. 8 to 10. Aheadspace 139 of the pressure-regulating chamber 106 is in fluidcommunication with a reversible air pump 140 via a pump outlet conduit142 interconnecting a headspace port 141 and a pump outlet 144. The pump140 has an arbitrary pump outlet 144 and a pump inlet 146. Since thepump is reversible, the pump outlet 144 and inlet 146 may be reversed.However, for the sake of clarity, the system 100 is described withreference to the arbitrary pump outlet and inlet designations definedabove.

The pump outlet conduit 142 comprises a conduit junction 148, whichconnects with corresponding pressure-regulating chambers 106 (each ofwhich are, in turn, connected to a corresponding ink reservoir 128) foreach color channel of the printhead 102. The conduit junction 148 thusenables a single air pump 140 to pressurize a plurality of chambers 106in parallel so as to prime each color channel of the printhead 102simultaneously using the same priming pressure.

The pump outlet conduit 142 has a second air vent 150, which equalizesthe pressure inside the chamber 106 with atmospheric pressure when thepump 140 is switched off. At atmospheric pressure, the float valve isclosed and ink 104 in the upstream ink conduit 134 equalizes with theset level of ink 104 in the chamber 106, as shown in FIG. 8.

On the outlet side of the printhead 102, the downstream ink conduit 138loops below the set level 110 and connects with a chamber inlet 152 of abubble-bursting chamber 154 positioned above the printhead 102. Anoptical sensor 156 is positioned adjacent the bubble-bursting chamber154 for sensing ink in the chamber. The sensor 156 provides a feedbacksignal 158 to the pump 140 when ink 104 is sensed in the chamber 154.The bubble-bursting chamber 154 is in fluid communication with an airchamber 160 via an air channel 162. The air chamber 160 is vented toatmosphere via a third air vent 163. An air outlet 164 defined in a baseof the air chamber 160 is in fluid communication with the pump inlet 146via an interconnecting pump inlet conduit 166. Bubble-bursting chambers154 (for each color channel of the printhead 102) and a common airchamber may be combined in one unit in the form of a bubble-burstingbox. A detailed description of the bubble-bursting box is providedbelow, although the schematic depiction in FIGS. 8 to 10 is sufficientfor the present purpose of describing printhead priming.

Thus, FIG. 8 shows the fluidics system prior to priming a dry printhead102. Ink 104 in the upstream ink conduit has equalized with the ink 104in the pressure-regulating chamber 106 by virtue of the second air vent150 in fluid communication with the headspace 139. When the pump 140 isswitched on (in a forward direction), air is pumped into thepressure-regulating chamber 106 and positively pressurizes the headspace139. The use of an air pump to pressurize the headspace 140 means thatpriming (and depriming) can be achieved using a single low-cost, robustcomponent. In contrast, inline peristaltic ink pumps are more costly andmay be prone to failure.

As shown in FIG. 9, the level of ink 104 in the pressure-regulatingchamber drops as the headspace 139 is pressurized and ink is forced upthe upstream ink conduit 134. Although the float valve opens the inletport 124 of the chamber 106 when the ink level drops, the ink is stillisolated from the ink reservoir 128 by virtue of a one-way check valve170. The check valve 170 is positioned in the ink supply conduit 130interconnecting the ink reservoir 128 and the inlet port 124, typicallyas part of the coupling to the ink reservoir. The check valve 170 allowsink to drain into the chamber 106, but does not allow ink to flow in theopposite direction. Hence, the positively pressurized headspace 139forces the ink 104 from the pressure-regulating chamber into the inkinlet 108 and through the printhead 102. To this end, it is importantthat the pressure-regulating chamber 106 contains sufficient ink 104 toprime the printhead 102.

Since the pump inlet 146 is in fluid communication with the ink outlet136, the ink outlet experiences a suction force so that ink 104 is bothpushed and pulled through the printhead 102 when the pump 140 isswitched on in the forward direction. Significantly, this pushing andpulling action minimizes any nozzle drooling during the primingoperation, irrespective of whether the printhead 102 is wet or dry priorto priming. This should be contrasted with arrangement shown in FIG. 11where the air outlet 164 is not in fluidic communication with the pumpinlet 146.

Referring again to FIG. 9, it can be seen that ink 104 is drawn throughthe printhead 102 during priming and enters the bubble-bursting chamber154 via the downstream ink conduit 138. When the optical sensor 156senses ink 104 in the bubble-bursting chamber, it sends a feedbacksignal 158 to the pump 140 (typically via a microprocessor, not shown),which instructs the pump to switch off. The optical sensor 156 andfeedback signal 158 guarantee that the printhead is fully primed whenthe pump 140 is switched off.

Turning now to FIG. 10, when the pump 140 is switched off, the checkvalve 170 opens and ink 104 in the pressure-regulating chamber 106returns to its set level 110 by virtue of more ink draining from the inkreservoir 128 and replenishing the ink used for priming. Additionally,some downstream ink is allowed to drain from the bubble-bursting chamber154 back through the printhead 102 and into the pressure-regulatingchamber 106 via the outlet port 126. However, the loop 180 in thedownstream conduit 138 prevents the printhead 102 from depriming. Thus,as shown in FIG. 10, ink 104 in the loop 180 equalizes with the setlevel 110 of ink in the pressure-regulating chamber 106 by virtue ofboth the upstream and downstream conduits 134 and 138 both being open toatmosphere via the air vents 150 and 163.

As an alternative to the loop 180 in the downstream conduit 138, anelectronically-controlled valve 172 may be positioned in the downstreamconduit so as to control the flow of ink therethrough. Such anarrangement is shown in FIG. 11. The valve 172 may be opened duringpriming and then closed simultaneously with the pump 140 being switchedoff so as to prevent drainage back through the printhead 102. Generally,the loop arrangement 180 is preferred to the electronically-controlledvalve 172, because it reduces the number of expensive componentsrequired in the fluidics system 100.

Referring again to FIG. 10, it will be seen that the portion of thedownstream conduit 138 from which ink has drained, as well as thebubble-bursting chamber 154, now contain a plurality of ink bubbles 174.These and other ink bubbles 174 are potentially problematic in futurepriming operations, as will be described in more detail below.

Printhead Depriming

In order to replace a printhead 102, the old printhead must first bedeprimed. Without such depriming, replacement of printheads would be anintolerably messy operation. FIG. 12 shows the fluidics system 100configured for a printhead depriming operation. In FIG. 12, the air pump140 is reversed and ink is drawn from the downstream conduit 138,through the printhead 102, and into the pressure-regulating chamber 106via the outlet port 126.

Since the level of ink 104 in the pressure-regulating chamber 106 nowrises, the float valve closes the inlet port 124, thereby isolating thechamber 106 from the ink reservoir 128. Hence, the float valve not onlyregulates the hydrostatic ink pressure during normal printing, but alsoserves to isolate the pressure-regulating chamber 106 from the inkreservoir 128 during depriming. This additional function of the floatvalve is important, because it prevents ink 104 from being sucked fromthe ink reservoir 128, into the pump outlet conduit 142, and into thepump 140 during depriming operations. Of course, the pressure-regulatingchamber should have sufficient capacity to accommodate the ink receivedtherein during depriming, as shown in FIG. 12.

Significantly, there is minimal or no ink wastage during depriming,because ink in the printhead 102 and downstream conduit 138 is allrecycled back into the pressure-regulating chamber 106.

Once all the ink in the downstream conduit 138, the printhead 102 andthe upstream conduit 134 has been drawn into the pressure-regulatingchamber 106, the pump 140 is switched off. The pump 140 is typicallyswitched off after predetermined period of time. Referring now to FIG.13, it can be seen that when the pump is switched off, some ink 104 fromthe pressure-regulating chamber 106 flows into the upstream conduit 134until it equalizes with the level of ink in the chamber 106. Since, atthis stage of depriming, the volume of ink 104 in thepressure-regulating chamber is relatively high, the ink equalizes at alevel higher than the set level 110, and the float valve keeps the inletport 124 closed. Hence, ink 104 is prevented from draining from the inkreservoir 128 into the upstream conduit 134, because the float valveisolates the ink reservoir. Again, this isolating function of the floatvalve during the printhead depriming operation is an important featureof the present fluidics system 100.

Still referring to FIG. 13, when the pump is switched off, the printhead102 may be removed and replaced with a replacement printhead.Significantly, a plurality of ink bubbles 174 are now present in boththe upstream conduit 134 and the downstream conduit 138. It is importantthat these ink bubbles 174 do not deleteriously affect subsequentpriming operations of the replacement printhead.

Replacement Printhead Priming

FIG. 14 shows a replacement printhead priming operation, followinginstallation of a replacement printhead 102 in the deprimed fluidicssystem shown in FIG. 13. For clarity, the replacement printhead is stilldesignated as a printhead 102 in the following discussion.

In contrast with the priming operation shown in FIGS. 8 to 10, there arenow ink bubbles 174 in the upstream and downstream conduits 134 and 138,which must be flushed through the system. However, since (as describedabove) the pump 140 both pushes and pulls ink 104 through the printhead102 during priming, the ink bubbles 174 in the upstream conduit 134 donot cause a significant increase in the requisite priming pressure andnozzle drooling is avoided.

As discussed above, printhead priming relies on accurate detection ofink 104 in the downstream ink conduit 138. When ink 104 is sensed in thedownstream conduit 138, the system ‘knows’ that the printhead 102 isprimed and the pump 140 may be switched off. Typically, an opticalsensor is used for the sensing the ink 104.

However, now that the downstream conduit 138 contains a plurality ofresidual ink bubbles 174, there is potential for phantom sensing of inkby the optical sensor. In other words, if the sensor senses ink bubbles174, rather than the advancing ink front from the body of ink 104 beingpumped through the system, then a feedback signal 158 may still be sentto the pump 140, even if the printhead 102 has not fully primed. It isimportant to minimize phantom sensing of ink caused by ink bubbles 174in the downstream conduit 138 so as to provide efficacious priming ofreplacement printheads. The pump 140 should be switched off only whenthe advancing ink front is sensed by the sensor, not when the residualtrapped ink bubbles 174 are sensed.

The bubble-bursting chamber 154 provides a means by which phantomsensing of ink bubbles 104 can be avoided. As will be described in moredetail below, the bubble-bursting chamber 154 is shaped so as to promotestretching and bursting of ink bubbles 174 entering the chamber via thechamber inlet 152. Generally, the bubble-bursting chamber 154 has alarger diameter and a shallower sidewall curvature than the downstreamconduit 138 feeding into chamber. This configuration means that the inkbubbles 174 entering via the chamber inlet 152 typically all burstinside the chamber 154 at or below a predetermined bubble-burstingpoint. The optical sensor 156 is positioned to sense ink above thebubble-bursting point, so that it does not sense any ink bubbles 174.Only the advancing ink front from the body of ink 104 is able to reachthe sensor 156 and trigger the feedback signal 158, which switches offthe pump 140. Once the pump 140 is switched off, the ink 104 drains tothe loop 180 and equalizes with the set level 110, as explained abovewith reference to FIG. 10.

Accordingly, the fluidics system 100 is suitable for a multitude offunctions, including controlling hydrostatic ink pressure during normalprinting, printhead priming, printhead depriming, and enabling printheadreplacement.

Further features of the bubble-bursting box and other individualcomponents of the fluidics system 100 will now be described in moredetail below.

Bubble-Bursting Box

Referring to FIGS. 15 to 17, the bubble-bursting box 200 is a two-partmolded unit comprising a chamber molding 202 and a cover molding 204having a polymeric sealing film 206 bonded thereto. The bubble-burstingbox 200 is a common unit for a plurality of ink channels so that onlyone box is required in a multi-channel printhead (see FIG. 20). Thebubble-bursting box 200 is configured for use with five ink channels, inaccordance with the printhead cartridge 2 described above. Hence, thechamber molding 202 comprises five bubble-bursting chambers 154A-E, eachhaving a respective chamber inlet 152 in base thereof. The chambermolding 202 further comprises a common air chamber 160 for eachbubble-bursting chamber 154.

Each bubble-bursting chamber 154 has curved sidewalls providing agenerally crescent-shaped chamber. This shape is ideally suited forexpanding and, hence, bursting ink bubbles 174 entering via respectivechamber inlets 152. An end chamber 154A comprises a main chamber 213 anda float ball chamber 214, which is configured for containing a floatball (not shown). The float ball chamber 214 is in fluid communicationwith the main chamber 213 so that the height of the float ballrepresents the height of ink in the main chamber 214 and, indeed, allthe other chambers 154B-E experiencing equal priming pressures. Sinceall chambers 154A-E are in fluid communication with the pump 140 andexperience equal priming pressures, only one chamber (e.g. the endchamber 154A) is required to have a sensor.

The optical sensor 156 (not shown in FIGS. 15 to 17) is positionedadjacent the float ball chamber 214 to sense the float ball above apredetermined bubble-bursting point. Accordingly, the float ball chamber214 is typically transparent or at least has a transparent windowenabling the optical sensor 156 to sense the float ball. Of course, afloat ball may alternatively not be utilized and the optical sensor 156may simply sense the ink itself.

The cover molding 204 comprises a plurality of air channels 162A-E, eachproviding fluid communication between a respective bubble-burstingchamber 154A-E and the common air chamber 160. Each air channel 162 hasa channel inlet 218 opening into a roof of a respective bubble-burstingchamber 154 and a channel outlet 219 opening into a roof of the commonchamber 160.

The air channels 162 are generally serpentine and each channel comprisestwo ink-trapping stomachs 220. Further, the cover molding 204 istypically comprised of a hydrophobic material so that the serpentine airchannels 162 have hydrophobic sidewalls. These features togetherminimize the possibility of ink in the bubble-bursting chambers 154A-Ebeing deposited into the common air chamber 160 via the air channels162A-E. Hence, the bubble-bursting box 200 is resilient to being tippedor even turned upside down. The air channels 162 defined in the covermolding 204 are sealed with the polymeric sealing film 206.

The air chamber 160 has an air outlet 164 defined in a base thereof.This air outlet 164 is connected to the pump inlet 146 via pump inletconduit 166 when the box 200 is installed in a printer. The air outlet164 is generally centrally positioned in the base of the air chamber 160and, as shown in FIGS. 15 and 16, the channel outlets 219 are offsetfrom the air outlet. By offsetting the channel outlets 219 from the airoutlet 164, it is ensured that, even if a small quantity of ink isdeposited into an ink collection zone in the air chamber 160, no ink canexit through the air outlet 164 and potentially foul the air pump 140.Additionally, a snorkel 224 extends towards the roof of the air chamber160 from the air outlet 164. The snorkel 224 increases the effectiveink-collecting volume of the air chamber 160. As shown in FIG. 15, thesnorkel 224 is relatively short, although this may lengthened ifdesired.

The cover molding 204 also has a plurality of air vents 163 definedtherein, which are positioned to vent the air chamber 160 to atmosphere.The microscopic air vents 163 are configured so that they can bedigitally punctured to provide an optimum priming pressure incombination with the air pump 140. The greater the number of vents 163that have been punctured, the lower the priming pressure will be. It isnot intended that users will puncture the vents 163; they are merelyprovided to facilitate manufacture of the box 200 in such a way that thebox may be ‘tuned’ for use with a variety of different printers, eachwith its own optimal priming pressure.

From the foregoing, it will be appreciated that the design of thebubble-bursting box 200 minimizes (and preferably prevents) any ink fromthe reaching the air pump 140 during priming. Thus, each bubble-burstingchamber 154 also functions as an expansion chamber, which canaccommodate a relatively large volume of ink. This minimizes thepossibility of ink reaching the air pump 140. It is important that theair pump 140 is protected in this way, because malfunctioning of the airpump would affect the overall operation of the printer. Even if the airpump 140 is robust enough to potential ink fouling, any color mixing inthe pump inlet conduit 166 and redistribution of mixed ink to thepressure-regulating chambers 106 would typically be catastrophic for theprinter.

In some embodiments, the bubble-bursting box may be used without the inksensor. Control of printhead priming may be achieved through use of atimer, which cooperates with the air pump 140 so as to limit itsoperation to a known priming (or depriming) period of time. Thebubble-bursting box 200 in the downstream ink conduit 138 safeguardsagainst any fouling of the pump 140 or color mixing in the event of, forexample, unexpected pressure surges during priming.

Pressure-Regulating Chamber

The pressure-regulating chamber 106 is shown in exploded form in FIG.18. The pressure-regulating chamber 106 comprises a main housing 250having the inlet port 124 and outlet port 126, and a cover portion 252having the headspace port 141. The cover portion 242 is fixed to themain housing 250 to form the chamber 106. The main housing 250 and coverportion 252 are typically comprised of molded plastics.

A pivot arm assembly comprises the arm 112 having a float cradle 113 atone end and a poppet mounting 115 at an opposite end. The float 116 ismounted in the float cradle 113 and the valve poppet 118 is mounted inthe poppet mounting 115. The arm 112 is pivotally mounted about thepivot 114, which is fixed between sidewalls of the main chamber 250. Thepivot 114 is positioned to provide maximum leverage force to the poppetvalve 118. All components of the pivot arm assembly are typically formedfrom molded plastics, with the exception of the stainless steel pivot112.

It will be appreciated that the pressure-regulating chamber 106 is arelatively inexpensive construction requiring no special manufacturingtechniques.

Print Engine with Fluidics Components

The print engine 3 typically has a bank of pressure-regulating chambers106 mounted towards a base thereof. By mounting the pressure-regulatingchambers 106 at the base of the print engine 3, there is minimal impacton the overall configuration, and particularly the overall height, ofthe print engine.

Each color channel usually has its own ink reservoir 128 andpressure-regulating chamber 106. Hence, the print engine 3 has five inkreservoirs 128 and five pressure-regulating chambers 106. Typical colorchannel configurations for the five-channel print engine 3 are CMYKK orCMYK(IR).

The pressure-regulating chambers 106, unlike the ink reservoirs 128 andthe print cartridge 2, are not intended to be user-replaceable in theprint engine 3.

FIG. 19 shows the print engine 3 comprising the bank ofpressure-regulating chambers 106, the bubble-bursting box 200 and aplurality of ink reservoirs 128 in the form of user-replaceable inkcartridges. Fluidic connections between these components are not shownin FIG. 19, but it will be appreciated that these connections are madewith suitable hoses in accordance with the fluidics system 100 herein.

Multi Channel Fluidic Connections

Whilst FIG. 19 shows the relative positioning of each component of thefluidics system in the printhead engine 3, FIG. 20 shows the fluidicconnections for a five channel printhead cartridge 2. Although FIG. 20shows fluidic connections for a five channel printhead, it will beappreciated that similar fluidic connections may be used for any desirednumber of color channels.

Thus, a bank of ink cartridges 128 supply ink via respective supplyconduits 130 to respective pressure-regulating chambers 106. Eachchamber 106 has a headspace in fluid communication with a respectivepump outlet conduit 142 which all feed into a conduit junction 148. Theconduit junction 148 is connected to an air outlet of the pump 140 via acommon junction conduit 149. The conduit junction 148 has the second airvent 150 defined therein.

Outlet ports of each chamber 106 are connected to an ink inlet of theprinthead cartridge 2 via upstream ink conduits 134. Downstream inkconduits 138 have one end connected to an ink outlet of the printheadcartridge 2 and an opposite end connected to respective bubble-burstingchambers of the bubble-bursting box 200. The pump inlet conduit 166connects the air outlet of the bubble-bursting box 200 to an air inletof the pump 140.

It will, of course, be appreciated that the present invention has beendescribed purely by way of example and that modifications of detail maybe made within the scope of the invention, which is defined by theaccompanying claims.

1. A method of replacing a printhead in an inkjet printer with minimalink wastage, said method comprising the steps of: (i) providing aprinthead comprising: an ink distribution manifold having an ink inletand an ink outlet; one or more printhead integrated circuits mounted onsaid manifold, each printhead integrated circuit comprising a pluralityof nozzles; (ii) providing an ink supply system comprising: an inkchamber in fluid communication with said ink inlet via an upstream inkline; a reversible air pump communicating with a headspace of said inkchamber; and a downstream ink line connected to said ink outlet; (ii)actuating said pump so as to negatively pressurize said headspace,thereby depriming said printhead by drawing ink from said downstream inkline and said printhead into said ink chamber; (iii) deactuating saidpump and allowing an ink level in said ink chamber to equalize with anink level in said upstream ink line; (iv) removing said printhead fromsaid printer, said removing including disconnecting said ink inlet andsaid ink outlet from respective upstream and downstream ink lines; (v)replacing said printhead with a replacement printhead, said replacingincluding connecting an ink inlet and an outlet inlet of saidreplacement printhead with respective upstream and downstream ink lines;(vi) actuating said pump so as to positively pressurize said headspace,thereby priming said printhead by drawing ink from said ink chamber,through said printhead and into said downstream ink line; and (vii)deactuating said pump and allowing an ink level in said ink chamber toequilibrate to a predetermined level.
 2. The method of claim 1, whereinsaid ink chamber has sufficient capacity to accommodate ink drawn intosaid chamber during said depriming step.
 3. The method of claim 1,wherein said downstream ink line comprises a loop section passing belowa level of ink in said ink chamber, wherein said predetermined ink levelin said ink chamber equalizes with an ink level in said loop sectionafter deactuation of said pump in step (vii).
 4. The method of claim 1,wherein said downstream ink line comprises an inlineelectronically-operated valve.
 5. The method of claim 1, furthercomprising the steps of: sensing ink in said downstream ink line using asensor; and deactuating said pump in response to sensing ink in saiddownstream ink line.
 6. The method of claim 5, wherein phantom sensingof ink caused by ink bubbles in said downstream ink line is minimized.7. The method of claim 6, wherein phantom sensing of ink is minimized bysensing for ink above a bubble-bursting point in a bubble-burstingchamber provided in said downstream ink line.
 8. The method of claim 1,wherein said ink chamber is a pressure-regulating chamber forcontrolling a hydrostatic pressure of ink supplied to said printheadduring normal printing.
 9. The method of claim 8, wherein saidpressure-regulating chamber comprises a float valve for maintaining apredetermined level of ink in said chamber, said float valve controllinga supply of ink to said chamber by an ink reservoir in fluidcommunication therewith.
 10. The method of claim 9, further comprisingthe step of: printing from said replacement printhead whilst controllingsaid hydrostatic pressure of ink using said pressure-regulating chamber.11. The method of claim 9, wherein said float valve isolates saidchamber from said ink reservoir during said depriming in step (ii). 12.The method of claim 9, wherein said ink reservoir comprises a checkvalve, said check valve isolating said chamber from said ink reservoirduring said priming in step (vi).